Definitions

Leukaemia cutis is a descriptive clinicopathological term for cutaneous infiltration by malignant leukaemic cells.
Myeloid sarcoma is a tumour mass of myeloid blasts outside the bone marrow; when it involves skin it overlaps clinically with leukaemia cutis but is a distinct haematological diagnosis.
“Chloroma” is a historic term for myeloid sarcoma, reflecting the green colour sometimes seen from myeloperoxidase-rich blasts.
Skin involvement may occur with AML, CML blast phase, myelodysplastic / myeloproliferative disorders and, less often, lymphoid leukaemias.
The key clinical message is urgency: new suspicious nodules in a patient with current or previous haematological malignancy need rapid biopsy and haematology liaison.

Clinical recognition

Lesions are variable: firm papules, nodules, plaques or tumours that may be skin-coloured, red-brown, violaceous, purpuric or occasionally ulcerated.
They may be solitary or multiple and can occur on trunk, limbs, head and neck, scalp, gingivae or sites of trauma.
Symptoms may be absent, which can make the lesions look deceptively benign.
Important mimics include cutaneous lymphoma, BPDCN, Sweet syndrome, infection, sarcoidosis, cutaneous metastasis and drug eruptions.
A history of AML, MDS/MPN, transplant, chemotherapy or unexplained cytopenias should lower the threshold for biopsy.

Biopsy should provide enough tissue for histology, immunohistochemistry and, where needed, flow cytometry or molecular/cytogenetic studies.
Common useful markers in myeloid sarcoma include CD43, CD68, myeloperoxidase, lysozyme, CD33, CD34 and CD117, interpreted in a full panel.
Initial systemic work-up is haematology-led and usually includes FBC, blood film, coagulation/biochemistry, marrow assessment and cytogenetic/molecular classification.
Clinicopathological details matter: provide previous haematology diagnosis, treatments, transplant status, blood counts and distribution of skin lesions.
If BPDCN, lymphoma or histiocytic neoplasm remains possible, specialist dermatopathology/haematopathology review is appropriate.

Management is determined by the underlying haematological diagnosis, disease timing and fitness for systemic therapy.
New myeloid sarcoma is generally treated using AML-type systemic strategies rather than local excision alone.
Radiotherapy can be useful for symptomatic, bulky, residual or locally problematic lesions when advised by haematology/oncology.
Surgery is mainly diagnostic or for selected local complications; excision of one lesion does not treat systemic disease risk.
Urgent MDT coordination is needed when skin lesions represent relapse after apparently successful marrow treatment.

Do not reassure multiple new violaceous papules in a patient with AML history as “benign angiomas” without considering relapse.
Do not assume normal-looking skin over a nodule excludes subcutaneous myeloid sarcoma.
Do not send a tiny superficial shave if the differential includes lymphoma, BPDCN or leukaemic infiltrate; tissue depth and ancillary testing matter.
Do not rely on local treatment alone unless haematology has excluded systemic disease and agreed a local-only strategy.
Do not conflate Sweet syndrome with leukaemia cutis: both can occur in myeloid disease, but management and histology differ.